Electromagnetic field analysis simulators are for performing EMC (Electro-Magnetic Compatibility) analysis on a PCB (Printed Circuit Board) on which electronic circuit modules are mounted. The EMC analysis is performed by various methods such as an FDTD (Finite-Difference Time-Domain) method, a moment method, and a TLM (Transmission-Line Matrix) method.
The FDTD method is for performing time-domain simulation on variations in the electromagnetic field of the analysis object. Specifically, the analysis object is divided into microscopic cells, and the electromagnetic fields of the cells are calculated at each analysis time step. The analysis time step in the FDTD method is dependent on the size of the cells. The maximum value of the analysis time step is limited by the size of the minimum cell, according to a stability condition for solutions of the simulation referred to as the Courant-Friedrichs-Lewy condition. The actual analysis time step in the FDTD method is typically set to be a microscopic value such as several tens of femtoseconds. Accordingly, an enormous number of calculations need to be performed to simulate temporal variations in the electromagnetic field between several nanoseconds and several tens of nanoseconds. For this reason, electromagnetic field analysis implemented with the FDTD method is typically performed by a parallel computation process with the use of plural processors, in order to reduce the calculation time.
Furthermore, the moment method is for obtaining variations in the electromagnetic field by deriving an integral equation of the analysis object with the use of a Maxwell equation and performing calculations in the frequency domain. Furthermore, the TLM method is for obtaining variations in the electromagnetic field of the analysis object in the time domain, similar to the FDTD method. Both in the moment method and the TLM method, an enormous number of calculations need to be performed in both the frequency domain and the time domain.
In recent years and continuing, various electronic circuit modules such as LSI (Large Scale Integration) are mounted on a printed circuit board. In order to improve the precision in EMC analysis of printed circuit boards, one approach is to perform electromagnetic field analysis by the FDTD method on the inside of the electronic circuit module such as LSI, in addition to performing the electromagnetic field analysis by the FDTD method on the substrate part including the wiring, the ground layer, and the power source layer. However, even more calculations need to be performed for the electromagnetic field analysis on the inside of electronic circuit module. Therefore, this approach is unrealistic for practical applications at present.
Accordingly, a coupled analysis simulation apparatus has been used for printed circuit boards on which electronic circuit modules such as LSI are mounted. Specifically, the coupled analysis simulation apparatus performs electromagnetic field analysis and circuit analysis in coordination with each other. The electromagnetic field analysis is performed by the FDTD method, etc., on elements other than electronic circuit modules such as wiring, the power source layer, and the ground layer. The circuit analysis is performed on electronic circuit modules such as LSI.
Signals are transmitted to the inside of the electronic circuit modules such as LSI, and to wiring on the substrate via terminals of the electronic circuit modules. The electromagnetic field in the wiring on the substrate is propagated to the inside of the electronic circuit modules via terminals of the electronic circuit modules.
In the conventional coupled analysis simulation apparatus, terminals of the electronic circuit modules are considered as virtual coupling devices for the coupled analysis, and the electronic circuit modules and the coupling devices are modeled. Accordingly, the coupled analysis is performed with the use of coupling devices that are virtual two-terminal devices that connect the analysis objects of the FDTD method to the analysis objects of the circuit analysis.
In a conventional coupling device, one terminal is connected to the wiring to which the electronic circuit module is connected, and the other terminal is connected to the nearest power source layer or ground layer to establish a current pathway.
In a conventional coupled analysis simulation apparatus, at each analysis time, a circuit analysis unit obtains the voltage value of the coupling device with the use of the current value of the coupling device, converts the obtained voltage value into an electric field value of the cell in which the coupling device is present, and passes the electric field value to an electromagnetic field analysis unit. Furthermore, the electromagnetic field analysis unit obtains the magnetic field from the electric field value of the cell in which the coupling device is present, converts the obtained magnetic field into a current value that flows into the coupling device, and passes the current value to the circuit analysis unit.
As described above, in the conventional technology, coupled analysis has been performed by repeating electromagnetic field analysis and circuit analysis while passing electric field values and current values of the coupling devices between the electromagnetic field analysis unit and the circuit analysis unit.
Patent document 1: Japanese Laid-Open Patent Application No. H11-153634
Patent document 2: Japanese Laid-Open Patent Application No. 2004-54642
Patent document 3: Japanese Laid-Open Patent Application No. 2008-217327
Patent document 4: International Publication 04/109560
Conventional coupled analysis simulation apparatuses have the following problems.
In a conventional coupling device, one terminal is connected to the wiring to which an electronic circuit module is connected, and the other terminal is connected to the nearest power source layer or ground layer. One of the terminals is connected to the nearest power source layer or ground layer for the purpose of establishing a current pathway at the part where the electronic circuit module is connected.
However, when coupling devices are connected between the wiring and the power source layer or ground layer, the current pathway may change from that of a case where the electronic circuit module is connected. Accordingly, a return path may not be accurately reproduced in the power source layer or ground layer.
Furthermore, when there are many connection parts (typically terminals) connecting the electronic circuit module to a conductive layer, it is difficult to recognize the current pathway inside the electronic circuit module. Thus, it is difficult to correctly determine where the coupling devices are to be connected, and therefore it may be difficult to model the coupling devices.
Even if the positions for connecting the coupling devices are correctly determined, the following problem may arise. That is, there may be cases where there are so many connection parts, such that the connection parts are blocked by other connection parts and the coupling devices may not be properly connected. When the coupling devices are not connected to the correct connection positions, it may not be possible to accurately reproduce the return path, even if the electromagnetic field analysis and the circuit analysis are performed in coordination with each other.